This invention relates generally to fuel injector systems utilizing a direct control needle valve, and more particularly a fluid sealing strategy to prevent mixing between fuel fluid and control fluid.
A common type of fuel injector system utilizes a direct control needle valve to open and close the nozzle outlets of the fuel injector. One end of the needle valve member is exposed to medium or low pressure control fluid in a needle control chamber, while a different portion is exposed to high or low fuel pressure in a nozzle chamber in a cyclic manner for each injection cycle. The nature of a needle valve is that extreme pressure differences are present between the needle control chamber and the nozzle chamber, where the needle valve member is positioned. These extreme pressure differences facilitate the lifting and closing of the needle valve and the resulting injection event. While the fuel acts as the pressurized fluid in the nozzle chamber, one class of fuel injectors use engine lubricating oil, or a similar fluid that is different from fuel, as the pressurized fluid in the needle control chamber.
A reoccurring issue with such an arrangement is the possibility of mixture between the oil in the needle control chamber and the fuel in the nozzle chamber. Because of the slight diametrical clearance between the needle valve member and its guide bore(s), migration of the fluids can occur in either direction as a result of the repetitive motion of the needle valve and the extreme difference in pressures between the oil and the fuel during different portions of the injection event. Depending on the timing in the injection cycle, the high-pressure location could be in the nozzle chamber or the needle control chamber. The migration of oil into the nozzle chamber can cause undesirable emissions when the fuel/oil mixture is injected into the combustion space. On the other hand, fuel migration into the needle control chamber can undermine the lubricating properties of the oil throughout the engine. Therefore, maintaining separation of the fluids is important to engine operation, performance and emissions.
Prior art has taught the use of an o-ring as an effective sealant against oil or fuel leakage. While an o-ring alone can provide a sufficient seal between the two fluids, research has shown that improperly applied o-rings typically fail long before the other parts of the fuel injector. The fuel injector""s extreme pressure, temperature requirements and high frequency of movements can prove to be fatal to the o-ring structure to the point that the o-ring becomes functionally useless. Furthermore, a degraded o-ring can provide a collection point for the oil or the fuel during the migration process, resulting in the potential to hasten the mixture problem.
One example of a fuel injector sealing strategy using an o-ring is taught by Stockner et al. in U.S. Pat. No. 5,901,686, entitled Fluid Seal For Cyclic High Pressures Within a Fuel Injector. While Stockner et al. teaches an effective sealing strategy in the plunger region, their strategy leaves room for improvement in the nozzle assembly portion of a directly controlled fuel injector.
The present invention is directed at overcoming one or more of the problems set forth above.
A fuel injection system includes of a source of control fluid, a source of fuel fluid and a fuel injector. The fuel injector is connected to the source of fuel fluid and control fluid, and has a direct control needle valve. The direct control needle valve has a needle valve member having a closing hydraulic surface exposed to the fluid pressure in a control chamber, and an opening hydraulic surface exposed to a fluid pressure in a fuel chamber. The direct control needle valve includes at least one guide region, at least one o-ring and at least one annulus positioned between the control fluid chamber and fuel chamber. A vent passage is disposed within the fuel injector and is connected to one of the at least one annulus.
In another aspect, a fuel injector includes an injector body that defines a control chamber, a fuel chamber, a control fluid vent passage and a fuel vent passage. Also, the fuel injector includes a direct control needle valve with a needle valve member having a closing hydraulic surface exposed to the fluid pressure in the control chamber, and an opening hydraulic surface exposed to a fluid pressure in the fuel chamber. At least one of the injector body and needle valve member define a first annulus fluidly connected to the control fluid vent passage, and a second annulus fluidly connected to the fuel vent passage.
In another aspect, a method of separating fluids in a fuel injector with a direct control needle valve includes a step of fluidly connecting a first annulus surrounding a needle valve member to a control fluid vent passage. A first guide region is positioned between a control chamber and the first annulus. A second annulus surrounding the needle valve member is fluidly connected to a fuel vent passage. A second guide region is positioned between a fuel chamber and the second annulus.